A series of cohort-sequential panel studies is proposed to examine changes in substance use and related factors across the life course and across historical period, using large nationally representative samples of high school graduates, from the end of high school through age 45. The study will examine social and environmental factors and processes, including life-course transitions that may explain change. The target samples are drawn randomly from graduating classes of high school senior participants from the Monitoring the Future (MTF) surveys (2400 respondents per cohort). Highly cost-efficient mailed surveys will be administered biennially one to twelve years past high school (to age 30), and once every five years thereafter (to age 45). Research objectives include: (1) monitoring substance use in important segments of the general population, including, in particular, American college students; (2) distinguishing among three different types of change taking place -- period, age, and cohort; and, (3) studying the causes, consequences, and developmental patterns associated with these different types of change. Each type has different sets of determinants and different timing of action, and all three types have been found to occur for most drugs. Factors that may explain historical trends and cohort differences will also be monitored. Additional objectives include documenting the natural history of drug use and related attitudes through middle adulthood, determining what transitions in social roles and social environments contribute to drug use and related attitudes, and determining what features of those roles and environments are most influential. The study will examine the importance of other hypothesized psychological, behavioral, and social determinants of drug use (including attitudes and beliefs about drugs, peer norms, counter-advertising, and role-modeling), as well as a range of potential consequences of drug use (including physical health, psychological well-being, status attainment, and role performance). The investigators will continue to facilitate use of MTF data by others for a variety of research purposes. Study results will have major implications for understanding and preventing drug use and abuse from adolescence through middle adulthood.